Combined effects of humic acids and salinity on solid-phase microextraction of DDT and chlorpyrifos, an estimator of their bioavailability

The unbound portion of dissolved hydrophobic environmental contaminants generally is presumed to be the most bioavailable to aquatic organisms. The effects of differing concentrations of Aldrich humic acid (HA) and salinity on the freely dissolved fraction of chlorpyrifos (CPF) and 4,4'-dichlorodiphenyltrichloroethane (DDT) in water were assessed through their relative uptake by solid-phase microextraction (SPME). This extraction method has been recently suggested as a valuable biomimetic tool. Increasing salinity (0-20 parts per thousand [parts per thousand]) alone had no effect on the uptake of DDT by the SPME fiber, but generally enhanced the SPME uptake of the more water soluble CPE Solid-phase microextraction uptake of DDT was decreased at an HA concentration of 10 mg/L, but 100 mg/L was required to decrease CPF uptake. Binding of CPF and DDT by HA was greatly reduced by the presence of salt at 5 to 20 parts per thousand. The extent of the HA and salinity effects appeared to be pesticide-dependent. These factors may ultimately impact the contaminant's environmental fate, transport, and bioavailability, for example, in estuarine situations.